1. Field of the Art
This invention relates to an optical system particularly suitable for use on simple low-cost photographic cameras or for lens-equipped photographic film packages with a simple camera mechanism intended for use with one roll of film only.
2. Description of the Prior Art
Generally, low-cost cameras for lens-equipped photographic film packages employ a single-element optical system from a standpoint of cost reduction or in some cases a two-element optical system from a standpoint of enhancing the picture quality. A conventional two-element optical system of this sort is described, for example, in U.S. Pat. No. 5,000,552, employing two lens elements, i.e., two positive meniscus lenses which are disposed symmetrically on the front and rear sides of an aperture stop.
In the case of simple and low-cost cameras or the lens-equipped photographic film packages as mentioned above, the shutter needs to be located closely to the aperture stop for the sake of shutter efficiency, and is necessarily of the so-called built-in type which is assembled integrally with the casing of a film package or camera. Therefore, in order to mount the two lens elements in positions on the front and rear sides of an aperture stop, it has been necessary to mount the respective elements in adjusted positions on the opposite sides of the aperture stop separately in different stages of a camera assembling process. This makes the camera assembling process complicated mainly because of the difficulty of aligning the optical axes of the separately mounted lens elements, which would suffer from deteriorations in performance quality if mounted in a misaligned state. Besides, the symmetrical lens disposition inherently suffers from increased spherical aberration in peripheral regions, resulting in unsatisfactorily low illumination by the lens.